1. Field of the Invention
The present invention relates to a temperature rise suppressing technique of a secondary battery charging apparatus, and to a technique effective for the use of, for example, a charge control circuit and a charge controlling semiconductor integrated circuit (IC) equipped with the charge control circuit.
2. Related Art
A secondary battery charging apparatus uses an IC equipped with a charge control circuit to control a charging current for suppressing an unusual temperature rise in a battery or the inner part of an apparatus. As an invention pertaining to such a charging apparatus, for example, the invention described in Japanese Patent Application Laid-Open Publication No. 2001-145274 exists.
The invention provides a temperature detection unit in the inner part or in the neighborhood of a heat generating part the temperature of which rises most or a part having the smallest temperature margin, and if an output of the temperature detection unit exceeds a predetermined temperature, then the invention controls the charging current to a secondary battery to decrease or stop the charging current.
Moreover, some charging apparatus are provided with the function of suppressing any temperature rises by providing a temperature detecting element on a chip in order to prevent the lowering of the reliability and further the occurrence of troubles of the charging apparatus owing to the heat generation of charge controlling ICs themselves for controlling charging currents.
The conventional temperature rise suppressing technique of a charge controlling IC is only a simple one to break a charging current by turning off a current controlling transistor when a chip temperature exceeds a predetermined temperature, such as 150° C.
The control method can suppress the chip temperature not to exceed the set temperature by repeating the cycle of: temperature rise—charging current breaking—temperature lowering—charging current reopening—temperature rise.
However, since the control method completely breaks the charging current when the chip temperature exceeds the predetermined temperature, such as 150° C., the control method has the apprehension of causing the chattering phenomenon of: current breaking—current reopening—current breaking—current reopening because a large current abruptly flows through a current controlling transistor at the time of reopening a charging current next owing to a delay in response of a feedback control loop. Moreover it becomes clear that there is the problem of the apprehension of causing the characteristic degradation of a secondary battery and therefore shortening a battery life owing to the sudden influx of a large current into the secondary battery at the time of current reopening.